Shear resistant wound dressing for use in vacuum wound therapy

ABSTRACT

A cover layer for a vacuum wound therapy dressing includes a backing layer formed from a flexible polymeric membrane and an adhesive layer for affixing the backing layer over a wound bed to provide a substantially fluid-tight seal around a perimeter of the wound bed. The cover layer is reinforced with a reinforcement layer extending to a peripheral region of the backing layer to distribute forces associated with evacuating a reservoir, as defined by or within the cover, to stimulate healing of the wound bed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. application Ser. No. 12/402,804, filed on Mar. 12, 2009 entitled “SHEAR RESISTANT WOUND DRESSING FOR USE IN VACUUM WOUND THERAPY”, which claims priority to, and the benefit of, under 35 U.S.C §119(e), U.S. Provisional Application No. 61/036,275, filed on Mar. 13, 2008 by Vitaris, the entire contents of which are being hereby incorporated by reference herein in their entirety and are to be considered a part of this specification.

BACKGROUND

1. Technical Field

The present disclosure relates generally to a wound dressing for treating an open wound with a vacuum wound therapy procedure. In particular, the disclosure relates to a wound dressing employing a reticulated or net-like reinforcement structure to protect the wound throughout the procedure.

2. Background of Related Art

The body's natural wound healing process is a complex series of events beginning at the moment of injury. Initially the body reacts by delivering proteins and other factors to the wound through the blood stream to minimize the damage. Blood clots to prevent blood loss while cells engulf bacteria and debris to carry it away from the wound site. Next, the body begins to repair itself in a stage of healing often referred to as the proliferate phase. This phase is characterized by the deposition granulation tissue in the wound bed. Granulation tissue provides a base structure over which cells may migrate inwardly from the periphery to close the wound. Finally the process ends as collagen gives strength to new tissue over time often forming a scar.

One technique for promoting the natural healing process, particularly, but not exclusively during the proliferate phase, is known as vacuum wound therapy (VWT). Application of a reduced pressure, e.g. sub-atmospheric, to a localized reservoir over a wound has been found to assist in closing the wound. The reduced pressure may be effective to promote blood flow to the area, to stimulate the formation of granulation tissue and the migration of healthy tissue over the wound by the natural process. Also a reduced pressure may assist in removing fluids exuding from the wound, which may inhibit bacterial growth. This technique has proven effective for chronic or non-healing wounds, but has also been used in for other purposes such as post-operative wound care.

The general VWT protocol provides for the introduction of a filler material into the wound to absorb exudates and promote fluid transport away from the wound bed. The wound filler may comprise such materials as non-reticulated foams, non-woven reinforcements or gauze. The wound and the absorbent wound filler material may then be covered by a flexible cover layer having an adhesive periphery that forms a substantially fluid tight seal with the healthy skin surrounding the wound. The cover layer thus defines a vacuum reservoir over the wound where a reduced pressure may be maintained over time by individual or cyclic evacuation procedures.

An aspect of concern in a VWT treatment is the management of forces generated in the dressing when a reduced pressure is applied. These forces may undesirably deform a flexible cover layer, draw the peri-wound margins into the wound and put the surrounding skin in tension. These same forces may significantly compress the absorbent filler such that it forms a rigid mass. In such a state, the filler adopts an increased tendency to adhere to the wound bed, restricts the fluid passages available for exudate transport and inhibits penetration of the reduced pressure there through. Accordingly, a need exists for a dressing suitable for use in a VWT procedure.

SUMMARY

The present disclosure describes a dressing for use in a vacuum wound therapy procedure to promote healing of a wound. The dressing includes a cover layer having an integrated support structure to manage forces associated with a VWT procedure. The cover layer includes a backing layer formed from a flexible polymeric membrane, an adhesive layer to affix the backing layer over a wound and provide to a seal around the wound bed, and a reticulated or net-like reinforcement layer affixed to the backing layer and extending to a peripheral region of the cover layer. The net-like reinforcement layer stiffens the cover layer and contributes to the ability of the cover layer to resist the deformation in the wound area commonly associated with a VWT procedure. Thus, the wound filler may be compressed to a minor degree such that it continues to provide exudate transport and vacuum penetration. The use of the net-like reinforcement layer may also lessen the degree to which the wound margin collapses, and may contribute to the manifestation of forces generated by the application of a reduced pressure as compression forces rather than shear forces. Compression forces applied to a wound is well known to be a beneficial wound treatment.

The reinforcement layer may be formed from such structures as a mesh of polyethylene terephthalatae fibers, apertured films and thermoplastic netting. The adhesive layer may be affixed to a peripheral region of the backing layer and may include an opening such that the adhesive layer does not extend to a central region of the cover layer. The adhesive layer may overlap a portion of the reinforcement layer such that the reinforcement layer is firmly affixed to the backing layer. Alternatively, the reinforcement layer may contain an appropriate adhesive coating to more firmly attach it to the backing layer. The backing layer may be formed from a polyurethane film having a thickness from about 0.8 mils to about 1.0 mils, and may include an aperture therein for facilitating connection of a vacuum port to the cover layer. The vacuum port may incorporate a filter screen defining a plurality of openings. The backing layer may be formed from a moisture vapor permeable membrane.

According to another aspect of the disclosure a wound dressing system includes a contact layer and an absorbent filler positioned in a wound bed and covered by a cover layer. A vacuum reservoir is defined between the cover layer and the wound bed. The cover layer includes a backing layer formed from a flexible polymeric membrane, an adhesive layer to affix the backing layer over a wound and provide to a seal around the wound bed, and a reinforcement layer affixed to the backing layer and extending to a peripheral region of the cover layer. A vacuum system is in fluid communication with the vacuum reservoir.

The contact layer may be formed from a conical apertured film to promote unidirectional flow of exudates from the wound. The absorbent filler material may include a single strand of a polyolefin filament. Also, the vacuum system may include a vacuum source, a collection canister and a one-way valve.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the present disclosure and, together with the detailed description of the embodiments given below, serve to explain the principles of the disclosure.

FIG. 1 is an exploded perspective view of a vacuum wound therapy system in accordance with the present disclosure;

FIG. 2 is an orthographic view of a wound facing side of the cover layer of FIG. 1;

FIG. 3 is an exploded cross sectional view taken along the line 3-3 of FIG. 2;

FIG. 4A is a cross sectional view of the vacuum wound therapy system of FIG. 1 installed over wound on a patient prior to application of a reduced pressure;

FIG. 4B is a cross sectional view of the vacuum wound therapy system of FIG. 1 installed over wound on a patient following an application of a reduced pressure;

FIG. 5 is a top plan view of a vacuum port of FIG. 1;

FIG. 6 is a perspective view of the vacuum port of FIG. 5;

FIG. 7 is a perspective view of an alternative embodiment of a vacuum port;

FIG. 8 is an exploded perspective view of an alternative embodiment of a vacuum port assembly including a portal member and an independent filter screen;

FIG. 8A is a perspective view of the filter screen of FIG. 8 in an alternate orientation;

FIG. 8B is a perspective view of an alternate embodiment of an independent filter screen;

FIG. 9 is a bottom plan view of the portal member of FIG. 8;

FIG. 10 is a partial cross sectional view of the vacuum port assembly assembled in a wound dressing; and

FIG. 11 is an exploded perspective view of an alternative embodiment of a vacuum port assembly including a treatment element.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The wound dressing of the present disclosure promotes healing of a wound by providing a reservoir over the wound where a reduced pressure may be maintained. The reservoir subjects the wound to a sub-atmospheric pressure to effectively draw wound fluid, including liquid exudates, from the wound without the continuous use of a vacuum pump. Hence, vacuum pressure may be applied once, or in varying intervals depending on the nature and severity of the wound. To facilitate fluid transport from the wound, a filler material may be included within the reservoir to promote the wicking of wound fluids subject to a reduced pressure. The use of a wound dressing in this manner has been found to promote healing by reducing the probability of infection, stimulating the deposition of granulation tissue and other beneficial processes. The wound dressing of the present disclosure includes a cover layer having a reinforcement structure to enhance the effect of a vacuum wound therapy treatment.

The attached figures illustrate exemplary embodiments of the present disclosure and are referenced to describe the embodiments depicted therein. Hereinafter, the disclosure will be described in detail by explaining the figures wherein like reference numerals represent like parts throughout the several views.

Referring initially to FIG. 1, a vacuum wound therapy system according to the present disclosure is depicted generally as 10 for use on a wound “w” surrounded by healthy skin “s.” The vacuum wound therapy system 10 includes a vacuum system 12 in fluid communication with a vacuum reservoir 14 (FIG. 4A) defined by or within wound dressing 16. The vacuum system 12 includes a vacuum source 18 coupled to the dressing 16 through a one-way valve 20 and a vacuum tube 24. A collection canister 28 may be provided for wound drainage and debris. The vacuum system 12 is adapted to provide a reduced pressure to the vacuum reservoir 14 appropriate to stimulate healing of the wound “w.” A more detailed description of an appropriate vacuum system 12 is found in commonly assigned U.S. Patent Application Publication 2007/0066946, the entire contents of which are incorporated herein by reference.

A vacuum port 30, depicted in greater detail in FIG. 5 and FIG. 6, may also be included to facilitate connection of the vacuum system 12 to the dressing 16. The vacuum port 30 may be configured as a rigid or semi-rigid, low-profile component adapted to receive the vacuum tube 24 in a releasable and fluid-tight manner. The vacuum port 30 may be configured to include a wide and flexible flange 32 about its perimeter. The flange 32 permits an adhesive to be attached to either an underside of flange 32 for securement to an outer surface of cover layer 44, or to a top side of flange 32 to provide for mounting to the underside of the reinforcement layer 46. Either configuration provides a mechanism for connecting to the dressing 16. A hollow interior of the vacuum port 30 provides fluid communication between the vacuum tube 24 and the reservoir 14 defined by or within dressing 16. A connector segment 33 extends above the flange 32 for facilitating connection with the vacuum tube 24. It is envisioned that because of the possible intimate proximity of the vacuum port 30 to either reservoir 14 or wound filler 38, the performance of vacuum port 30 may be enhanced by the incorporation of a filter screen 58 as depicted in FIG. 6 and FIG. 7. Filter screen 58 may inhibit the migration of large particles that may otherwise be drawn into the vacuum port 30 and consequently create a restriction or blockage of the vacuum tube 24. The filter screen 58 may be integral to the configuration of the vacuum port 30 as part of the port flange 32. The filter screen 58 may include a number of openings, each smaller than a cross-sectional area of the vacuum tube 24 or the opening in the vacuum port 30 adapted to receive the vacuum tube 24, and collectively greater than the cross-sectional area of vacuum tube 24 or the opening in the vacuum port 30 adapted to receive the vacuum tube 24. For example, the filter screen 58 of vacuum port 30 may include four relatively large openings, while the filter screen 58A of vacuum port 30A depicted in FIG. 7 may include six relatively small openings. The openings in the filter screens 58, 58A are dimensioned to minimize the passage of tissue particles of a predetermined dimension through the respective vacuum port 30, 30A.

Another alternate embodiment of a vacuum port is depicted generally as 30B in FIGS. 8, 9, 10 and 11. Vacuum port 30B may be configured to accept a filter screen 59 or 60 as a distinct or independently manufactured component as depicted in FIGS. 8, 10 and 11. An opening or cavity 31 depicted in the plan view of FIG. 9 and shown in phantom in FIG. 8 on an underside of vacuum port 30B may be adapted to permit filter screen 59 to be permanently bonded therein such that filter screen 59 is substantially flush with the underside of vacuum port 30B. Alternatively, filter screen 60 may be bonded to the opening on the underside of vacuum port 30B. Filter screen may 60 includes a generally flat base 62 through which the openings 65 extend, and a pair lips 64 projecting from the base 62 along opposite edges of the filter screen 60. The lips 64 may be dimensioned to be flush with a patient facing under surface of the flange when received within the cavity 31. Alternatively the lips 64 may extend beyond the under surface of the flange to extend beyond the cavity 31 in the portal member 30B as depicted in FIG. 10. Filter screen 60 may exhibit an increased surface area available for bonding within cavity 31 of vacuum port 30B. Filter screen 60 may be secured within cavity 31 by bonding, cements, adhesives or the like. In one embodiment, filter screen 62 is positioned within cavity 31 with lips 64 facing toward the wound (FIGS. 8 and 10). In another embodiment, filter screen 62 is positioned within lips 64 facing toward vacuum port 30B and away from the wound (FIG. 8A). In another embodiment, base 62 is devoid of lips 64 as shown in FIG. 8B, and is substantially planar.

It is also envisioned that filter screens 59 and 60 may be provided in combination with a treatment element 61 comprising a therapeutic material as depicted in FIG. 11. Treatment element 61 may be inserted between filter screens 59, 60 and may secured to vacuum port 30B by an appropriate adhesive bond. The treatment element 61 and filter screens 59, 60 may define an insert for reception into cavity or opening 31 on the underside of portal member 30B. This arrangement may provide a convenient method of treating the wound exudate as it is drawn from the wound “w.” Treatment element 61 may comprise fibrous or granulated materials contained in a porous container or wrap to facilitate placement between filter screens 59 and 60. Treatment element 61 may include materials such as activated charcoal or other odor control or neutralizing substances. Treatment element 61 may include anti-bacterials such as polyhexamethylene biguanide (PHMB). Also, antimicrobials such as ionic metals or biguinides may be included to reduce the bio-burden of the exudate or microbials within the exudate as the exudate is drawn in to a collection canister 28. In the alternative, filter screens 59, 60 may comprise charcoal, antimicrobials, anti-odor substances.

Vacuum tube 30 may be configured to accept a variety of tubing geometries such as round, oblong or elliptical. Vacuum port 30 may be provided as a pre-affixed component of dressing 16, as part of vacuum system 12 or entirely independently. Also vacuum port 30 may not be necessary depending on the configuration of dressing 16.

Wound dressing 16 generally includes a contact layer 34, filler 38 and a reinforced cover layer 40. Reinforced cover layer 40 may be formed from a composite including a backing layer 44, a reinforcement layer 46 and an adhesive layer 48. Each layer of wound dressing 16 is described in greater detail below.

Contact layer 34 may be sufficiently conformable to be positioned in direct contact with an irregularly shaped surface of a wound bed “w.” A thin film of polyethylene or other suitable non-adherent material may form the contact layer 34 to limit the adherence of filler 38 and other substances to the wound “w.” Apertures or perforations in the film permit fluids to pass through the contact layer 34, allowing for the sub-atmospheric pressure to penetrate into the wound “w” and for exudates to flow freely out of the wound “w.” By selecting an appropriate film material, the passage of wound exudate through contact layer 34 may be controlled so as to be substantially unidirectional to prevent wound exudate from flowing back into the wound. To promote a unidirectional flow, a conical apertured film, such as those provided by Tredegar Film Products of Richmond, Va., may be selected for forming contact layer 34. This type of film is arranged with apertures positioned at the peaks of cone shaped formations in the film material such that exudate encounters the film as an array of micro-funnels in one direction and an array of collecting basins in the other. Though it is depicted in a square configuration, the shape of the contact layer 34 can be customized to better suit the wound geometry. Unidirectional flow of exudates may also be promoted by the selection of other materials including a lamination of layers having varying absorptive characteristics. One exemplary material, which may be used as a contact layer is sold under the trademark XEROFLO® by Kendall Corp., a division of Covidien.

Filler 38 may be arranged over contact layer 34 to fill wound “w” to the level of the surrounding healthy skin “s” or may over-fill the wound “w” as depicted in FIG. 4A. An absorbent material such as non-woven gauze or reticulated foam may be used for filler 38 to trap or transport any exudate that migrates through contact layer 34. An antimicrobial dressing sold under the trademark KERLIX® by Kendall Corp., a division of Covidien, may be suitable for use as filler 38. To prevent adhesion to the wound “w,” the filler 38 may also comprise a material configured such that any stray fibers do not tend to protrude through apertures of contact layer 34 where they may become engulfed by newly forming granulation tissue. One particular type of material exhibiting this characteristic is often referred to as “tow.” The manufacturing process for synthetic fibers often includes an extrusion of an indeterminate length of continuous filaments, which are spun together to form fibers. It is the continuous lengths of un-spun filaments which are referred to as tow. A single length of tow formed from a hydrophobic material such as polyolefin may be laid in the wound bed “w” to form filler 38. This arrangement allows for a complete removal of filler 38 when the dressing 16 is changed without re-injuring the wound “w.”

Cover layer 40 may be placed over the wound “w” enclosing the contact layer 34 and filler 38 therein. The periphery of cover layer 40 extends laterally beyond the perimeter of the wound bed “w” so as to contact the healthy skin “s” to form a seal over the wound “w.” As depicted in FIG. 2, adhesive layer 48 may extend to the periphery of cover layer 40 to provide the seal with the use of a medical-grade, pressure-sensitive adhesive. The adhesive layer 48 may be adapted to provide a fluid-tight and bacteria-tight seal around a peripheral region of dressing 16 such that exudate cannot escape through the edges of the dressing 16 and external air and contaminants may not enter the wound area. To provide such a barrier, the adhesive layer 48 may, for example, be on the order of 1.0 to 10 mils thick depending on the adhesive used. In general, a high peal-strength adhesive may be used to resist inadvertent lift-off, roll or “flagging,” i.e., a failure of the dressing to adhere to itself or the patient, at the edges of the cover layer 40. The adhesive defining the adhesive layer 48 may include, but is not limited to, medical grade acrylics, rubber base or silicone adhesives. Preferably, those adhesives included with the dressing sold under the trademark Polyskin II Transparent Dressings by Kendall Corp., a division of Covidien, may be used. Adhesive layer 48 forms a continuous band around the peripheral region of cover layer 40, but contains an opening such that the adhesive layer does not extend inwardly to the central areas of cover layer 40.

As depicted in FIG. 3, reinforcement layer 46 may overlap adhesive layer 48 at an outer edge such that an outer periphery of reinforcement layer 46 is firmly affixed to backing layer 44. Reinforcement layer 46 extends to a peripheral region of cover layer 40, but not necessarily to an outer perimeter of the cover layer 40. Reinforcement layer 46, particularly any portion not overlapping the adhesive layer 48, may be affixed to backing layer 44 with a light coat of an adhesive 57 applied to the appropriate side of the reinforcement layer 46 or the backing layer 44. A portion of a wound facing side 52 of the reinforcement layer 46 carries no adhesive to prevent adhesion of the cover layer 40 to the filler 38. An aperture 54 extends through the reinforcement layer 46 to permit fluid communication between the reservoir 14 and vacuum system 12.

The reinforcement layer 46 may comprise a mesh of polyethylene terephtalate (PET) fibers, which offer good liquid resistance making it suitable for use in a moist wound environment. PET fibers may be used to form woven or non-woven reinforcements having large pore sizes. Some PET reinforcement manufacturing methods provide for interlinking the fiber junctions to yield a mesh that is flexible in multiple directions and also does not unravel when cut. One such method is known as hydro-entanglement. PET reinforcements thus manufactured tend to have a high shear stiffness that may be useful in reinforcing cover layer 40. One exemplary material, which may be suitable for incorporation into reinforcement layer 46, is sold under the trademark Sontara® by DuPont. Alternatively, reinforcement layer 46 may be formed from another reinforcement or mesh structure having suitable shear stiffness. Examples of suitable structures include extruded netting and apertured films. Suitable materials for use in such alternate structures include PET, polyethylene, nylon and polypropylene. Additionally, woven structures may be used for reinforcement layer 46. Acceptable woven materials may include cotton gauze, woven acetate and nylon.

Extending to the periphery of the cover layer 40 is backing layer 44. Backing layer 44 provides a substrate to which reinforcement layer 46 and adhesive layer 48 may be affixed. An aperture 56 extends through the backing layer 44 to permit fluid communication between the reservoir 14 and vacuum system 12. Backing layer 44 may be formed from a flexible polymeric membrane to serve as a fluid barrier to allow for a sub-atmospheric pressure to be established in vacuum reservoir 14, and also as a microbial barrier preventing contaminants from entering the wound area. For example, backing layer 44 may comprise a polyurethane film having a thickness from about 0.8 mils to about 1.0 mil. Preferably, the backing layer 44 is formed from a moisture vapor permeable membrane to promote the exchange of oxygen and moisture vapor between the wound site and the atmosphere. One exemplary material is a transparent membrane sold under the trade name POLYSKIN® II by Kendall Corp., a division of Covidien. Other materials which may be suitable for use in a backing layer include the thin films marketed under the names TEGADERM™ by 3M of St. Paul, Minn. and OPSITE™ by Smith and Nephew PLC of London, UK. Reinforcement layer 46 may be configured so as not to impede the transmission of moisture vapor by including, for example, a large pore size.

As seen in FIG. 4A, reservoir 14 is defined by or within wound dressing 16 when applied to the skin Filler 38 may be included to fill the reservoir 14. Evacuating atmospheric gasses from the reservoir 14 may impart a tendency for cover layer 40 to flatten against the wound “w” as depicted in FIG. 4B. This tendency of cover layer 40 to deform may draw the peri-wound margins into the wound “w” and put the surrounding skin “s” in tension. This tendency may be counteracted or resisted by the shear stiffness in reinforcement layer 46 such that the cover layer 40 may better main its shape. Because reinforcement layer 46 extends to a peripheral region of cover layer 40 and backing layer 44 anchored to healthy skin “s,” the forces associated with evacuating reservoir 14 may be transferred beyond the perimeter of the wound “w,” and may be manifested as compression forces. Thus reinforcement layer 46 reinforces cover layer 40 and vacuum reservoir 14.

A central region of reinforcement layer 46 may be devoid of an adhesive coating, such that the reinforcement layer 46 may not tend to adhere to or disturb filler 38, particularly as the reduced pressure is removed from reservoir 14. Reinforcement layer 46 thus further protects wound “w” to promote healing throughout the evacuation cycles of a VWT procedure.

Although the foregoing disclosure has been described in some detail by way of illustration and example, for purposes of clarity or understanding, it will be obvious that certain changes and modifications may be practiced within the scope of the appended claims. 

What is claimed is:
 1. A negative pressure wound therapy dressing comprising: a backing layer comprising a flexible polymeric membrane, the backing layer including an inner wound facing side, an outer side opposite the wound facing side, and an aperture extending through the backing layer; an adhesive disposed on the inner wound facing side of the backing layer; a reinforcement layer disposed on the inner wound facing side of the backing layer; an absorbent filler including an inner wound facing side, wherein the absorbent filler is configured to be in fluid communication with the reinforcement layer and configured to collect exudate removed from a wound; and a perforated wound contact layer configured to be in direct contact with the wound, wherein the absorbent filler is configured to be positioned over the wound contact layer; and a vacuum port configured to be fluidically connected, via a tube, to a negative pressure source, wherein the vacuum port comprises: a flange having an underside and a top side, wherein the underside of the flange has an opening positioned over the aperture in the backing layer and the underside of the flange is positioned on the outer side of the backing layer; and a connector extending above the flange, the connector configured to be connected to the tube; and a filter screen positioned underneath the vacuum port, the filter screen configured to prevent migration of particles into the vacuum port.
 2. The dressing according to claim 1, wherein the reinforcement layer comprises a network of interlinked fibers that comprises a mesh formed from polyethylene terephthalate fibers (PET).
 3. The dressing according to claim 1, wherein the adhesive is affixed to a peripheral region of the backing layer and includes an opening such that the adhesive does not extend to a central region of the dressing.
 4. The dressing according to claim 3, wherein the adhesive overlaps a portion of the reinforcement layer such that the reinforcement layer is affixed to the backing layer.
 5. The dressing according to claim 1, wherein the backing layer comprises a polyurethane film having a thickness from about 0.8 mils to about 1.0 mils.
 6. The dressing according to claim 1, wherein the backing layer comprises a moisture vapor permeable membrane.
 7. The dressing according to claim 1, wherein the reinforcement layer is substantially liquid resistant.
 8. The dressing according to claim 1, wherein the reinforcement layer comprises a mesh formed from fibers.
 9. The dressing according to claim 8, wherein the fibers are interlinked.
 10. The dressing according to claim 1, wherein the absorbent filler comprises material configured to trap exudate.
 11. The dressing according to claim 1 in combination with the negative pressure source configured to provide reduced pressure to the wound.
 12. The dressing according to claim 1, wherein the wound contact layer is configured to promote a substantially unidirectional flow of fluid so as to prevent exudate removed from the wound from flowing back into the wound when vacuum is applied to the wound.
 13. The dressing according to claim 1, wherein the filter screen is configured to extend across the opening in the underside of the vacuum port such that, when vacuum is applied to the wound, fluid passing through the fluid passage of the vacuum port passes through the filter screen.
 14. The dressing according to claim 1, wherein the backing layer, the reinforcement layer and the wound contact layer have a square shape.
 15. The dressing according to claim 1, wherein the aperture in the backing layer is located in a central region of the backing layer.
 16. The dressing according to claim 1, wherein the reinforcement layer has stiffness suitable to resist deformation of the dressing during application of vacuum wound therapy to the wound.
 17. The dressing according to claim 1, wherein the reinforcement layer extends to a peripheral region of the backing layer.
 18. The dressing according to claim 1, wherein the reinforcement layer comprises an aperture that extends through the reinforcement layer to permit fluid communication between the wound and the negative pressure source. 